Electronic still camera having an image sensor in which reading and clearing is performed sequentially

ABSTRACT

An electronic still camera comprises an image sensor which allows each of its horizontal lines to be individually specified so that a video signal contained in each specified horizontal line can be read, a storage circuit for storing the video signal read from the image sensor, a selecting circuit for selecting a high-speed continuous shooting mode, and a controlling circuit for executing, when the high-speed continuous shooting mode is selected by the selecting circuit, control to effect a high-speed reading for reading the video signal from the image sensor by thinning out the horizontal lines of the image sensor, and to cause the storage circuit to store video signals for a plurality of pictures obtained by the high-speed reading.

This application is a divisional of application Ser. No. 08/991,917,filed Dec. 16, 1997, now U.S. Pat. No. 6,518,999, issued Feb. 11, 2003,which is a continuation of application Ser. No. 08/389,543, filed Feb.15, 1995, now abandoned, which is a continuation of application Ser. No.07/998,821, filed Dec. 30, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic still camera and, moreparticularly, to high-speed continuous shooting suitable for theelectronic still camera.

2. Description of the Related Art

An electronic still camera (also called the still video camera) hasconventionally been provided with a continuous shooting mode, and theelectronic shutter function of an image sensor such as a CCD has beenutilized to increase the continuous shooting speed of the electronicstill camera. As compared with a silver-salt camera, such a continuousshooting function is useful for the electronic still camera which usesan erasable and re-recordable medium.

To gain the continuous shooting speed, various proposals have been made.A primary factor which determines the continuous shooting speed is theoperating time of mechanisms. The continuous shooting speed is notaffected by the shutter of the electronic still camera since anelectronic shutter is utilized. However, since a magnetic head ismechanically arranged, the time required to move the magnetic headinfluences the continuous shooting speed.

To solve the problem, it has been proposed to provide an electronicstill camera having an image memory. In such an electronic still camera,image data read from an image sensor are thinned out to prepare imagedata having a data size reduced to 1/16 or 1/25 of the original datasize, and the thus-prepared image data are stored in the image memory sothat the image data are sequentially subjected to continuous shooting. Aseries of data which has been prepared in this manner is read from theimage memory and written to a video floppy disk. At this time, since a1V (vertical scanning) period is necessarily needed to complete areading from the image sensor, the 1V period constitutes a primaryfactor which determines the continuous shooting speed.

Regarding the high-speed continuous shooting, the above-describedelectronic still camera has the problems described in the followingparagraphs (1) to (3).

(1) Since the 1V period ( 1/60 second) is required to complete a readingfrom the image sensor, it is difficult to shoot a rapidly movingsubject.

(2) Even while a subject is not moving, recording is performed, so thata number of useless exposures are produced.

(3) If a plurality of exposures which have been recorded as one pictureare reproduced, the motion of a subject is difficult to grasp.

SUMMARY OF THE INVENTION

An object of the present invention which has been made in the light ofthe above-described problems is to provide an electronic still camerawhich is capable of effecting continuous shooting at a far higher speed,which does not produce a large number of useless exposures duringrecording, and which is capable of reproducing an image so that themotion of a subject can be easily grasped.

To achieve the above-described object, according to several aspects ofthe present invention, there is provided an electronic still camerawhich is arranged as described in the following paragraphs (1), (2) and(3).

(1) In accordance with one aspect of the present invention, there isprovided an electronic still camera which comprises an image sensorwhich allows each of its horizontal lines to be individually specifiedso that a video signal contained in each specified horizontal line canbe read, memory means for storing the video signal read from the imagesensor, selecting means for selecting a high-speed continuous shootingmode, and controlling means for executing, when the high-speedcontinuous shooting mode is selected by the selecting means, control toeffect a high-speed reading for reading the video signal from the imagesensor by thinning out the horizontal lines of the image sensor, and tocause the memory means to store video signals for a plurality ofpictures obtained by the high-speed reading.

(2) In accordance with another aspect of the present invention, there isprovided an electronic still camera which comprises an image sensorwhich allows each of its horizontal lines to be individually specifiedso that a video signal contained in each specified horizontal line canbe read, memory means for storing the video signal read from the imagesensor, selecting means for selecting a high-speed continuous shootingmode, decision means for comparing a video signal for one picture whichhas been read from the image sensor with a video signal for one picturewhich was immediately previously stored in the memory means, anddetermining whether both of the video signals represent a substantiallyidentical image, and controlling means for executing, when thehigh-speed continuous shooting mode is selected by the selecting means,control to effect a high-speed reading for reading the video signal fromthe image sensor by sampling the horizontal lines of the image sensor,and, if the decision means determines that a read picture issubstantially identical to a picture immediately previously stored inthe memory means, to discard a video signal indicative of the readpicture.

(3) In accordance with another aspect of the present invention, theelectronic still camera described in the above paragraph (1) or (2)further comprises reproducing means for reproducing a series ofpictures, which are stored with the high-speed continuous mode selected,so that the pictures are reproduced at predetermined time intervals byone at a time.

According to the arrangements described in the above paragraphs (1), (2)and (3), if the high-speed continuous shooting mode is selected, duringreading from the image sensor, the horizontal lines are thinned out andhigh-speed reading is performed. According to the arrangements describedin the above paragraphs (2) and (3), while the high-speed continuousshooting mode is selected, if a subject does not move, a video signalread from the image sensor is discarded. According to the arrangementdescribed in the above paragraph (3), pictures which are recorded in thehigh-speed continuous mode are reproduced at predetermined timeintervals by one at a time.

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof a preferred embodiment of the present invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of an embodiment of the present invention;

FIG. 2 is a block diagram of the counters of the clock generatingcircuit shown in FIG. 1;

FIG. 3 is an explanatory view of the image sensor shown in FIG. 1;

FIG. 4 is a timing chart showing the timing of selection of an addressand an iris;

FIG. 5 is a timing chart showing the operation of each counter shown inFIG. 2;

FIG. 6 is a view showing a picture formed by sixteen-exposure continuousshooting;

FIG. 7 is a block diagram of the memory shown in FIG. 1;

FIG. 8 is a timing chart showing the operation of each of the blocks ofFIG. 7; and

FIGS. 9( a), 9(b), 9(c) and 9(d) are views showing different manners ofreproduction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described belowwith reference to the accompanying drawings.

FIG. 1 is a block diagram schematically showing the preferred embodimentof an electronic still camera according to the present invention.

The electronic still camera shown in FIG. 1 includes a lens 1, adiaphragm 2 which utilizes a turret type of diaphragm (not shown), animage sensor 3, such as a general MOS sensor, the horizontal lines ofwhich can be read on a line-by-line basis, a sample-and-hold gamma (SHG)circuit 4 for sampling and holding image data read from the image sensor3 and executing gamma correction of the sampled and held image data, anA-D converter 5 for converting analog image data into digital imagedata, a memory 6, using a RAM or the like, for storing image data forsixteen exposures, a digital signal processor (DSP) 7 for executingsignal processing, a D-A converter 8 for converting digital image datainto analog image data, a reproducing circuit 9, a recording circuit 10,and a recording-reproducing head 11. Reference numeral 12 denotes avideo floppy disk which serves as a magnetic recording medium.

The shown electronic still camera also includes a clock generatingcircuit 13 for controlling the timing of each of the image sensor 3, theSHG 4, the A-D converter 5, the memory 6, the DSP 7 and the D-Aconverter 8. The shown electronic still camera also includes a systemcontroller 14, using a microcomputer or the like, for executing modeswitching and sequential control, an encoder 15 which operates during areproducing mode, a flash unit 16, switches 17 and 18 each of whichswitches according to switching between the reproducing mode and arecording mode, a light measuring (AE) sensor 19, a flashing controllingsensor 20, a liquid-crystal display 21 for providing visual display asto various modes, a track number and the like, an LED 22 which blinksduring self-timer shooting, a shooting-mode selecting switch 23 forselecting a single shooting mode, a self-timer shooting mode, ahigh-speed continuous shooting (H-Cont) mode or an extremely-high-speedcontinuous shooting (SH-Cont) mode, a flash mode switch 24 for selecting“flash on”, “flash off” or “auto-flash”, switches SW1 25 and SW2 26which serve as trigger switches for initiating a recording sequence, anda disk drive motor 27.

First of all, a normal recording sequence will be described below.

When a release button (not shown) is pressed to turn on the switch SW125, the disk drive motor 27 is started up to initiate recording on thevideo floppy disk 12. The system controller 14 reads measured-light datafrom the AE sensor 19 and performs a light-measurement computation. Whenthe release button is further pressed to turn on the switch SW2 26, thediaphragm 2 is driven up to an aperture value determined by thelight-measurement computation. Then, exposure of the image sensor 3 isexecuted at a predetermined electronic shutter speed.

The image data stored in the image sensor 3 is read in accordance with aclock signal generated by the clock generating circuit 13. The SHG 4samples and holds the read image data and executes gamma correction ofthe sampled and held image data. The analog image data outputted fromthe SHG 4 is converted into digital image data by A-D conversionexecuted by the A-D converter 5. The digital image data is passedthrough the memory 6 and is subjected to signal processing in the DSP 7.The processed digital image signal is subjected to D-A conversion in theD-A converter 8, and the analog output of the D-A converter 8 isrecorded on the video floppy disk 12 through the switch 17 and therecording-reproducing head 11.

The recording sequence executed during the single shooting mode is asdescribed above. High-speed continuous shooting is realized by repeatingthe recording sequence while the switch SW2 26 is on.

FIG. 2 is a block diagram showing counters disposed in the clockgenerating circuit 13 for controlling the image sensor 3. FIG. 3 is anexplanatory view showing the image sensor 3 the horizontal lines ofwhich can be read on a line-by-line basis.

Referring to FIG. 3, five hundred effective lines are arranged in thevertical direction, and image data are read from two adjacent lines in azigzag manner through the two adjacent lines during one horizontalperiod (hereinafter referred to as “1H period”). Among the lines shownin FIG. 3, each pair of adjacent lines constitutes one horizontal line,that is, each pair of lines 1 and 2, lines 3 and 4, . . . , and lines499 and 500 constitutes one horizontal line.

Referring to FIG. 2, the clock generating circuit 13 includes a counter(V.TV counter) 201 which serves as a vertical counter and counts anelectronic shutter speed, a decoder 202 for generating timing from anoutput from the counter 201, a horizontal counter 203, a decoder 204 forgenerating timing from an output from each of the counters 201 and 203,a start address 205 for setting the address of a line at which readingis to be started, an end address 206 for setting the address of a lineat which reading is to be ended, an address counter 207, an iris counter208, an address-end detector 209, an address-iris selector 210, and aniris-end detector 211.

FIG. 4 is a timing chart showing the timing of selection of an addressand an iris during the first 1H period. The term “address” representsthat image data is read from a line specified by an address, and theterm “iris” represents that a line specified by an iris is cleared.

The time taken until a line specified by the iris is read according tothe address constitutes a shutter speed (time). This shutter speed(time) is determined by an integer multiple of one horizontal period(H).

FIG. 5 is a timing chart showing the state of operation of each of thecounters shown in FIG. 2. In FIG. 5, there is shown a case where thehorizontal lines of one picture are thinned out to ¼, and a verticalsynchronizing signal (NVD) is added for reference.

First, a reading start address and a reading end address arerespectively preset in the start address 205 and the end address 206shown in FIG. 2. Simultaneously, “¼” is set as the rate at which thehorizontal lines of one picture are thinned out. Then, a multiple of “H”which is equivalent to a shutter speed is set in the V.TV counter 201.The timing of “H” is generated from an output from the H counter 203,and an iris is set in address buses B1 to B9 as shown in FIG. 4. The Hcounter 203 counts up at 260FH (FH: horizontal frequency), and iscleared when a count of 260 is reached. The V.TV counter 201 counts downby one each time the H counter 203 reaches the count of 260.

In the meantime, since an increment signal (INC) is supplied from theH.V decoder 204 at the timing shown in FIG. 4, the iris counter 208counts up by two during each 1H period. In the case of start address 1,the first and second lines (1 and 2) are cleared during the first “H”,and subsequently the iris counter 208 counts up by four in the order of5 and 6, 9 and 10 and so on.

The V.TV counter 201 is made to count down in this manner, and when acount of 0 is reached, the image sensor 3 proceeds from an image-datastore enable state to an image-data read enable state. In this case, theaddress counter 207 starts sequential counting at a start address. Forexample, if TV=20H, the signals shown in FIG. 4 are as follows: AISELand DMSEL are outputted from the H.V decoder 204, then switched by theaddress-iris selector 210, and then outputted to the address buses B1 toB9 so that DUMMY=0, ADR=1, IRIS=81, ADR+1=2 and IRIS+1=82 are obtained.

The address counter 207 similarly counts up in accordance with theincrement signal. Then, a freeze gate signal (FRZ_GATE) (1) is outputtedso that the image data for the two lines selected in the above-describedmanner are stored in the memory 6 of FIG. 1. The image data read out inthis manner are stored in an area on the memory 6 which corresponds to apart (1) of the picture shown in FIG. 6.

The H counter 203 and the V counter 202 are made to count up to continueaddress counting and iris counting.

If the iris-end detector 211 detects that the iris counter 208 hascounted up to a count indicative of the end of the reading, the iris-enddetector 211 outputs an iris count end signal (IEND) so that theincrement signal (INC) is inhibited from being outputted to the iriscounter 208.

Similarly, if the address-end detector 209 detects that the addresscounter 207 has counted up to a count indicative of the end of thereading, the address-end detector 209 outputs an address count endsignal (AEND) so that the increment signal (INC) is inhibited from beingoutputted to the address counter 207.

Then, at the time of the end of reading of the last pixel on the lastline, FRZ_GATE is returned from its lower level to its high level andthe operation of storing image data for one exposure in the area (1) ofthe memory 6 is completed.

By repeating the above-described operation, further image data arestored in the respective areas (2) to (6) of the memory 6. If theoperation of storing the image data in the areas (1) to (16) of thememory 6 is completed, the disk drive motor 27 is started up, and afterthe rotation thereof becomes stable, reading from the memory 6 isstarted. The image data read from the memory 6 are recorded on the videofloppy disk 12 through the DSP 7, the D-A converter 8, the recordingcircuit 10 and the recording-reproducing head 11 in accordance with asignal REC_GATE. In this manner, sixteen exposures are recorded on onetrack by the high-speed continuous shooting.

In the present embodiment, the reading time required to complete areading from the image sensor 3 is determined by how the horizontallines are thinned out. If “¼” is set as the rate at which the horizontallines of one picture are thinned out, the reading time becomes (¼)V(vertical period) which is constant at approximately 4 msec.Accordingly, a continuous shooting speed is determined by a shutterspeed, that is, a value which is preset in the V.TV counter 201.

In the present embodiment, although a thin-out operation in the verticaldirection is realized by reading image data from the image sensor 3every fourth line, a thin-out operation in the horizontal direction isrealized by reducing the conversion clock frequency of the A-D converter5 to ¼ or by thinning out image data at the time of writing into thememory 6.

FIG. 7 is a block diagram of the memory 6. The memory 6 includes amemory 701 for storing image data, a controller 702 for controllingwriting, reading and addresses, a comparator 703 for making a comparisonbetween input image data and read image data, and a counter 704 which isset to its count-enable state when the output of the comparator 703 isat its high level (when the difference between the input image data andthe read image data is above a certain level).

FIG. 8 is a timing chart showing writing to and reading from the memory6 as well as the operation of the comparator 703.

The operation of the memory 6 will be described below with reference toFIGS. 7 and 8.

In brief, image data, which is read from the image sensor 3 each timeone exposure is performed during continuous shooting, is compared withthe previous data stored in the memory 6, and if no large variation isdetected, the read data is not stored in the memory 6.

Referring to FIG. 8, at time (i), image data is outputted from the imagesensor 3 and is stored in the area (1) on the memory 6. At the time (ii)of FIG. 8, while the next image data outputted from the image sensor 3is being written into the area (2) on the memory 6, the controller 702reads the image data stored in the area (1) at the time (i) and causesthe comparator 703 to make a comparison between the aforesaid next imagedata and the read image data. If a difference above a predeterminedvalue is detected, one count enable pulse is outputted to the counter704. If the value of the counter 704 is above the predetermined value,it is determined that a substantial variation has occurred between therespective images captured as the first and second exposures duringcontinuous shooting. At this time, a signal (Next Write) for advancing awrite address to the next location ((2)→(3)) is outputted from thecounter 704 to the controller 702.

At the time (iii) of FIG. 8, writing of image data to the area (3) onthe memory 6 and reading of the image data from the area (2) areperformed, and a comparison between them is made.

If the value of the counter 704 is below the predetermined value and novariation in image is detected, the signal Next Write is not set to itshigh level.

At the time (iv), the controller 702 executes control so that writing ofimage data to the area (3) of the memory 6 and reading of image datafrom the area (2) are again performed. Thus, frozen images for sixteenexposures (pictures) are obtained.

In the above-described manner, while writing to and reading from thememory 6 are being performed in parallel, a comparison is made betweencurrently written image data and image data written immediately beforethe currently written image data. If no substantial variation isdetected between particular written image data and the previous writtenimage data, the particular written image data is overridden andoverwritten (discarded) during the next cycle of image-data reading.Accordingly, it is possible to achieve high-speed continuous shootingwhich permits recording of a continuously and visibly varying image.

Reproduction of the images recorded through the continuous shooting inthe above-described manner will be described below. If the images arereproduced by a general still video player, it is possible to reproducethe sixteen pictures as a multiple picture in an instant.

During recording in the high-speed continuous shooting mode, thecontinuous shooting speed (interval time) and the number of theexposures recorded through the continuous shooting are recorded in auser area of ID (identification) data.

An operation executed during the reproducing mode will be describedbelow with reference to FIG. 1.

The disk drive motor 27 is driven to rotate the video floppy disk 12.When the rotation of the video floppy disk 12 becomes stable, areproduced signal enters the reproducing circuit 9 through the recordingreproducing head 11 and a corresponding one of the contacts of theswitch 17. The reproduced signal is transmitted to the A-D converter 5in the form of a luminance signal (Y) and a chrominance signal (C). Eachof the luminance and chrominance signals (Y) and (C) is converted into adigital signal, and the digital signal is stored in the memory 6.

During this time, an ID signal is also reproduced so that the continuousshooting speed and the number of the exposures recorded through thecontinuous shooting can be identified.

Since it is necessary to insert borders between the images of therespective exposures while image data are being stored in the memory 6,data indicative of the borders (black or gray) are written into thememory 6 at horizontal-line locations determined by the number of theexposures.

When data for a series of continuous pictures are frozen in theabove-described manner, the driving of the disk drive motor 27 isstopped. Then, the data are read from the memory 6 and outputted to amonitor through the DSP 7, the D-A converter 8 and the encoder 15.

FIGS. 9( a) to 9(d) show different manners of reproduction on themonitor.

FIG. 9( a) shows the manner in which image data are reproduced in theorder in which the image data were recorded.

FIG. 9( b) shows the manner in which the image data are rearranged, asin the shown order, and reproduced in a frozen state so that a user caneasily make a comparison between an arbitrary exposure and the nextexposure, as in the case of stop-motion photography of a batting formfor baseball.

FIG. 9( c) shows the manner in which image data for one exposure isreproduced on the monitor as one picture at a time.

FIG. 9( d) shows the manner in which the screen of the monitor isprovided with a white mask of shape which extends along the four sidesof the monitor screen so that a reduced picture can be reproduced. Thereproduction of the reduced picture is intended to prevent a coarseimage from being reproduced. In the above-described embodiment, such acoarse image is reproduced if image data is restored as is thinned out,because simple thin-out processing is only used.

In the manner of reproduction shown in each of FIGS. 9( c) and 9(d),since it is possible to know a shooting speed at the time ofreproduction of the ID signal, if reproduction is executed at a speedcorresponding to the shooting speed, it is possible to continuouslyreproduce a series of exposures, whereby the motion of a subject can bereproduced as a flash motion.

Although, in the above-described embodiment, sixteen exposures arerecorded as one continuous picture, it is also possible to adopt anarrangement which allows the user to specify a desired number ofexposures such as nine exposures or twenty-five exposures. The intervaltime between successive exposures during photography may be newly set ifa variation of a subject can be predicted or if it is necessary toobserve variations which occur in the subject at predetermined timeintervals. Since the range of variations of the interval time is limitedin relation to the range of shutter speeds, it is desirable to issue awarning to the user when the interval time is to be reduced. Althoughthe video floppy disk 12 is used as a recording medium, other recordingmedia such as a memory card may be used.

In the above-described embodiment, after images for sixteen exposureshave been stored in the memory 6, recording on the video floppy disk 12is performed. However, it is possible to adopt another arrangement inwhich if the switch SW2 26 is turned off before all the images forsixteen exposures are stored, recording is executed at that time. It ispossible to adopt still another arrangement. For example, while theswitch SW2 26 is on, the operation of storing image data in the memory 6is continued, and image data for the first exposure is overwritten withimage data for the seventeenth exposure so that the latest sixteenimages are always stored. If the switch SW2 26 is turned off, the latestsixteen images at that time are recorded from the memory 6 onto thevideo floppy disk 12. Although, in the above-described embodiment, thecomparator 703 uses a fixed level, it is also possible to adopt anarrangement which allows a photographer to set an arbitrary level.

During reproduction, if data indicative of borders are to be writteninto the memory 6 during storage in the memory 6 on the basis of thenumber of exposures, it is desirable to make the borders thicker thanthose written during recording. Although the above description refers toa technique for sequentially reproducing by one at a time, it is alsopossible to adopt a far more effective arrangement which is capable ofsimultaneously reproducing four continuous exposures so that the usercan select an arbitrary exposure from among the four continuousexposures.

In the above-described embodiment, a series of image data is oncetransferred to the video floppy disk 12 and is then reproducedtherefrom. However, the present invention is not limited to thisarrangement. For example, the present invention can be practiced in theform of outputting data read from a memory without using a video floppydisk. In the case of such a form, recording means may be externallyprovided or a reproduced output may be used as a soft copy.

As is apparent from the foregoing description, in accordance with theabove-described embodiment, since high-speed reading is executed bythinning out the horizontal lines of one picture, it is possible toachieve far higher-speed continuous shooting.

In accordance with the above-described embodiment, if similar imagescontinue, the corresponding video signals are discarded, so that it ispossible to achieve high-speed continuous shooting which does notproduce an useless exposure.

In accordance with the above-described embodiment, since images capturedthrough the high-speed continuous shooting are reproduced atpredetermined time intervals by one exposure at a time, it is possibleto reproduce the motion of a subject as a flash motion.

1. An electronic still camera comprising: an image sensor which allowseach of its horizontal lines to be individually specified so that animage signal contained in each specified horizontal line can be readsequentially after a plurality of horizontal lines are clearedsequentially; memory which stores the image signal read from said imagesensor; selecting device which selects a high-speed shooting mode forreading two or more image planes; and controller which executes, whenthe high-speed shooting mode is selected by said selecting device,control to effect a high-speed reading for reading the image signal fromsaid image sensor by decreasing the horizontal lines of said imagesensor after a plurality of horizontal lines are cleared sequentially,and to cause said memory means to store image signals for a plurality ofpictures obtained by the high-speed reading.